Sahih Al Bukhari (502)

حدثنا مالك {أتينا إلى النبي صلى الله عليه وسلم ونحن شببة متقاربون فأقمنا عنده عشرين يوما وليلة وكان رسول الله صلى الله عليه وسلم رحيما رفيقا فلما ظن أنا قد اشتهينا أهلنا أو قد اشتقنا سألنا عمن تركنا بعدنا فأخبرناه قال ارجعوا إلى أهليكم فأقيموا فيهم وعلموهم ومروهم وذكر أشياء أحفظها أو لا أحفظها وصلوا كما رأيتموني أصلي فإذا حضرت الصلاة فليؤذن لكم أحدكم وليؤمكم أكبركم}

Malik (may Allah be pleased with him) narrated: We came to the Prophet (peace be upon him) and stayed with him for twenty days and nights. We were all young and of about the same age. The Prophet (peace be upon him) was very kind and merciful. When he realized our longing for our families, he asked about our homes and the people there and we told him. Then he asked us to go back to our families and stay with them and teach them (the religion) and to order them to do good things. He also mentioned some other things which I have (remembered or) forgotten. The Prophet (peace be upon him) then added, “Pray as you have seen me praying and when it is the time for the prayer one of you should pronounce the Adhan and the oldest of you should lead the prayer.